Technical Field
Embodiments of the subject matter disclosed herein generally relate to protecting a towed marine survey system from damage or malfunction due to lines entangled with survey equipment, or, more specifically, to a cutter device configured to diminish or prevent line entanglements.
Discussion of the Background
During marine surveys (e.g., seismic and/or electromagnetic), various pieces of equipment are towed through water. Some pieces of equipment are directly employed to gather information about an explored structure under the seafloor (e.g., sources configured to generate waves, receivers configured to detect waves reflected by the structure, recorders configured to store data related to the detected waves), while other pieces of equipment are configured to ensure that the former ones are towed and arranged according to a predetermined survey geometry. These other pieces of equipment include cables, steering equipment, deflectors, floaters, etc. For example, a marine survey system may include plural (e.g., twelve) streamers (i.e., cables housing receivers, such as hydrophones) about 10 km long and having about 100 m distance there-between, perpendicular to the towing direction. A customary survey speed is about 5 kts.
While towed through water, the marine survey system may encounter various items floating freely, such as damaged or lost fishing gear, or equipment in use or left to be retrieved, etc. These items frequently have attached lines (i.e., strings, ropes or nets) that may slide along the system's cables until eventually they either get entangled with an obstacle or drift away. The obstacles may be cable-mounted equipment or depth-decreasing end sections of cables. FIG. 1 illustrates, as an example, a streamer steering device 110 (known as a “bird”) mounted on a streamer 120 and having spurious lines 130 (only some labeled) entangled thereon.
The entangled lines increase drag, make it difficult to control a cable's shape and relative location within the towed system, lead to cables spinning and twisting, or damage cable sections and the cable-mounted equipment. Removing entangled lines and making repairs that may become necessary due to them are costly in terms of time and personnel.
Accordingly, it is desirable to provide devices and methods that would diminish or prevent line entanglement.